This paper extends to electrical machines the thermodynamics and heat transfer optimization approach that has been developed for heat engines. Four models of thermodynamically irreversible electrical motors with heat transfer to the ambient are proposed and optimized : general reversible motor in series with its resistance, induction motor with transformer, synchronous motor with transformer and direct current motor. The conversion efficiency at maximum power is 1/2. When, as in specific applications, the operating temperature of the windings must not exceed a specified level, the power output is lower and the efficiency higher. In the case of an electrical power generator it is shown that the generator and the heat engine that drives it can be optimized separately for maximum power.